Microelectrical mechanical structure (MEMS) optical modulator and optical display system

ABSTRACT

A microelectrical mechanical out-of-plane thermal buckle-beam actuator is capable of providing transverse-plane movement of shutters. The actuator includes a pair of structural anchors secured to a substrate and one or more thermal buckle-beams secured at respective base ends to the anchors. Each buckle-beam extends substantially parallel to and spaced-apart from the substrate and is releasable from the substrate at points other than at the anchors. The thermal buckle-beam actuators are suitable for use in a microelectrical mechanical optical display system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/064,410, filed Feb. 22, 2005, which is a divisional of U.S. patentapplication Ser. No. 10/873,070, filed Jun. 21, 2004, which is acontinuation of U.S. patent application Ser. No. 09/702,585 now U.S.Pat. No. 6,775,048, issued Aug. 10, 2004, each of which is herebyincorporated by reference in its entirety.

This application is also related to co-pending U.S. application Ser. No.10/872,741 filed on Jun. 21, 2004, and entitled “MicroelectricalMechanical Structure (MEMS) Optical Modulator and Optical DisplaySystem” which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to optical display systems and, inparticular, to a display system that employs a microelectricalmechanical system (MEMS) optical modulator.

BACKGROUND OF THE INVENTION

Flat panel optical display systems, such as liquid crystal displays, arewell known and widely used. Many such displays (e.g., liquid crystaldisplays) require polarized illumination light. Typically, polarizationof illumination light greatly attenuates the light, thereby resulting indisplays with decreased brightness, or require relatively expensiveoptical components. Moreover, such displays commonly have relatively lowcontrast ratios, which decreases image clarity and overall imagequality. Furthermore, such displays typically require complex ordifficult manufacturing processes.

SUMMARY OF THE INVENTION

To address such shortcomings, the present invention includes amicroelectrical mechanical optical display system that employsmicroelectrical mechanical system (MEMS) actuators to modulate light. Asis known in the art, MEMS actuators provide control of very smallcomponents that are formed on semiconductor substrates by conventionalsemiconductor (e.g., CMOS) fabrication processes. MEMS systems andactuators are sometimes referred to as micromachined systems-on-a-chip.

In one implementation, a MEMS optical display system according to thepresent invention includes an illumination source for providingillumination light, a collimating lens for receiving the illuminationlight and forming from it collimated illumination light, and aconverging microlens array having an array of lenslets that converge thecollimated illumination light. The converging microlens array directsthe illumination light to a microelectrical mechanical system (MEMS)optical modulator.

The MEMS optical modulator includes, for example, a planar substratethrough which multiple pixel apertures extend and multiple MEMSactuators that support and selectively position MEMS shutters over theapertures. A MEMS actuator and MEMS shutter, together with acorresponding aperture, correspond to a pixel. The light from theconverging microlens array is focused through the apertures and isselectively modulated according to the positioning of the MEMS shuttersby the MEMS actuators, thereby to impart image information on theillumination light. The light is then passed to a diffused transmissivedisplay screen by a projection microlens array.

In alternative implementations, a MEMS optical device module can beformed with at least, for example, a converging microlens array, a MEMSoptical modulator, and a projection microlens array. MEMS opticaldisplay systems according to the present invention can be formed frommultiple such modules that are arranged in arrays and combined withlight sources, collimating optics, and display screens.

A MEMS optical display system according to the present invention isoperable without polarized illumination light, thereby eliminating thelight attenuation or expense of the polarizing illumination light. Inaddition, light can be completely blocked or modulated by the opaqueMEMS shutters, thereby providing display images with very high contrastratios. Furthermore, such MEMS optical modulators can be manufactured byconventional CMOS circuit manufacturing processes.

Additional objects and advantages of the present invention will beapparent from the detailed description of the preferred embodimentthereof, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-15 are cross-section views of a general multi-user MEMS processknown in the prior art for fabricating microelectrical mechanicaldevices. Cross-hatching is omitted to improve clarity of the prior artstructure and process depicted.

FIG. 16 is a diagrammatic side view of one implementation of amicroelectrical mechanical (MEMS) optical display system according tothe present invention.

FIG. 17 is a diagrammatic side view of a MEMS optical device module.

FIG. 18 is a diagrammatic side view of a modular optical device thatincludes an array of multiple MEMS optical device modules of FIG. 17.

FIG. 19 is another implementation of a microelectrical mechanical (MEMS)optical display system according to the present invention.

FIGS. 20 and 21 are front view of an exemplary MEMS actuator inrespective activated and relaxed states for a controlling MEMS shutter.

FIG. 22 is yet another implementation of a microelectrical mechanical(MEMS) optical display system according to the present invention.

FIG. 23 is a diagrammatic plan view of a microelectrical mechanicalout-of-plane thermal buckle-beam actuator.

FIG. 24 is a diagrammatic side view of the actuator of FIG. 23 in arelaxed stated.

FIG. 25 is a diagrammatic side view of the actuator of FIG. 23 in anactivated state.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

To assist with understanding the present invention, the generalprocedure for fabricating micromechanical devices using the MUMPsprocess is explained with reference to FIGS. 1-15.

The MUMPs process provides three-layers of conformal polysilicon thatare etched to create a desired physical structure. The first layer,designated POLY 0, is coupled to a supporting wafer, and the second andthird layers, POLY1 and POLY2, respectively, are mechanical layers thatcan be separated from underlying structure by the use of sacrificiallayers that separate layers and are removed during the process.

The accompanying figures show a general process for building amicro-motor as provided by the MEMS Technology Applications Center, 3021Cornwallis Road, Research Triangle Park, N.C.

The MUMPs process begins with a 100 mm n-type silicon wafer 10. Thewafer surface is heavily doped with phosphorus in a standard diffusionfurnace using POCI 3 as the dopant source. This reduces chargefeed-through to the silicon from electrostatic devices subsequentlymounted on the wafer. Next, a 600 nm low-stress Low Pressure ChemicalVapor Deposition (LPCVD) silicon nitride layer 12 is deposited on thesilicon as an electrical isolation layer. The silicon wafer and siliconnitride layer form a substrate.

Next, a 500 nm LPCVD polysilicon film—POLY 0 14—is deposited onto thesubstrate. The POLY 0 layer 14 is then patterned by photolithography; aprocess that includes coating the POLY 0 layer with a photoresist 16,exposing the photoresist with a mask (not shown) and developing theexposed photoresist to create the desired etch mask for subsequentpattern transfer into the POLY 0 layer (FIG. 2). After patterning thephotoresist, the POLY 0 layer 14 is etched in a Reactive Ion Etch (RIE)system (FIG. 3).

With reference to FIG. 4, a 2.0 μm phosphosilicate glass (PSG)sacrificial layer 18 is deposited by LPCVD onto the POLY 0 layer 14 andexposed portions of the nitride layer 102. This PSG layer, referred toherein as a First Oxide, is removed at the end of the process to freethe first mechanical layer of polysilicon, POLY1 (described below) fromits underlying structure; namely, POLY 0 and the silicon nitride layers.This sacrificial layer is lithographically patterned with a DIMPLES maskto form dimples 20 in the First Oxide layer by RIE (FIG. 5) at a depthof 750 nm. The wafer is then patterned with a third mask layer, ANCHOR1,and etched (FIG. 6) to provide anchor holes 22 that extend through theFirst Oxide layer to the POLY 0 layer. The ANCHOR 1 holes will be filledin the next step by the POLY1 layer 24.

After the ANCHOR1 etch, the first structural layer of polysilicon(POLY1) 24 is deposited at a thickness of 2.0 μm. A thin 200 nm PSGlayer 26 is then deposited over the POLY1 layer 24 and the wafer isannealed (FIG. 7) to dope the POLY1 layer with phosphorus from the PSGlayers. The anneal also reduces stresses in the POLY1 layer. The POLY1and PSG masking layers 24, 26 are lithographically patterned to form thestructure of the POLY1 layer. After etching the POLY1 layer (FIG. 8),the photoresist is stripped and the remaining oxide mask is removed byRIE.

After the POLY1 layer 24 is etched, a second PSG layer (hereinafter“Second Oxide”) 28 is deposited (FIG. 9). The Second Oxide is patternedusing two different etch masks with different objectives.

First, a POLY1_POLY2_VIA etch (depicted at 30) provides for etch holesin the Second Oxide down to the POLY1 layer 24. This etch provide amechanical and electrical connection between the POLY1 layer and asubsequent POLY2 layer. The POLY1_POLY2_VIA layer is lithographicallypatterned and etched by RIE (FIG. 10).

Second an ANCHOR2 etch (depicted at 32) is provided to etch both theFirst and Second Oxide layers 18, 28 and POLY1 layer 24 in one step(FIG. 11). For the ANCHOR2 etch, the Second Oxide layer islithographically patterned and etched by RIE in the same way as thePOLY1_POLY2_VIA etch. FIG. 11 shows the wafer cross section after bothPOLY1_POLY2_VIA and ANCHOR2 etches have been completed.

A second structural layer, POLY2, 34 is then deposited at a thickness of1.5 μm, followed by a deposition of 200 nm of PSG. The wafer is thenannealed to dope the POLY2 layer and reduce its residual film stresses.Next the POLY2 layer is lithographically patterned with a seventh maskand the PSG and POLY2 layers are etched by RIE. The photoresist can thenbe stripped and the masking oxide is removed (FIG. 13).

The final deposited layer in the MUMPs process is a 0.5 μm metal layer36 that provides for probing, bonding, electrical routing and highlyreflective mirror surfaces. The wafer is patterned lithographically withthe eighth mask and the metal is deposited and patterned using alift-off technique. The final, unreleased exemplary structure is shownin FIG. 14.

Lastly, the wafers undergo sacrificial release and test using knownmethods. FIG. 15 shows the device after the sacrificial oxides have beenreleased.

In preferred embodiments, the device of the present invention isfabricated by the MUMPs process in accordance with the steps describedabove. However, the device of the present invention does not employ thespecific masks shown in the general process of FIGS. 1-15, but ratheremploys masks specific to the structure of the present invention. Also,the steps described above for the MUMPs process may change as dictatedby the MEMS Technology Applications Center. The fabrication process isnot a part of the present invention and is only one of several processesthat can be used to make the present invention.

FIG. 16 is a diagrammatic side view of a microelectrical mechanicalstructure (MEMS) optical display system 50 according to the presentinvention. Display system 50 includes a light source 52 and reflector 54that direct illumination light to a collimator lens 58. A convergingmicrolens array 60 having a two-dimensional array of lenslets 62 (onlyone dimension shown) received the collimated light and focuses it towarda microelectrical mechanical structure (MEMS) optical modulator 70.Microlens array 60 could be formed as a molded array of plastic lensesor an array of holographic lenses, also referred to as hololenses, ormay be an assembled array of conventional glass lenses.

MEMS optical modulator 70 has a two-dimensional array of microelectricalmechanical structure (MEMS) shutters 72 that are positioned adjacentcorresponding apertures 74 through a microelectrical mechanicalstructure (MEMS) substrate 76, as described below in greater detail.Each MEMS shutter 72 corresponds to a picture element or pixel and isseparately controllable by a display controller 78 to block or passillumination light according to an image control signal (not shown),thereby to form a display image. For example, each MEMS shutter 72 couldocclude its aperture 74 in inverse proportion to the brightness of thecorresponding pixel for a given pixel period, or each MEMS shutter 72could occlude it aperture 74 for an occlusion period that is inverselyproportional to the brightness of the corresponding pixel.

A projection microlens array 80 having a two-dimensional array oflenslets 82 (only one dimension shown) receives the display image lightand projects it toward a rear surface 84 of a transmissive displayscreen 86 for viewing by an observer 88. Projection microlens array 80may be of a construction analogous to microlens array 60, and could beidentical to it to minimize manufacturing tooling costs. Alternatively,projection microlens array 80 could enlarge or reduce the optical fieldso that it provides a desired image size on transmissive display screen86, and display screen 86 can be a diffuse display screen.

MEMS optical display system 50 has a number of advantages over commonlyavailable liquid crystal displays. For example, MEMS optical modulator70 does not require that the illumination light be polarized, incontrast to the typical operation of liquid crystal cells. Thiseliminates the expense and light attenuation that typically accompaniespolarization. Moreover, MEMS optical modulator 70 can pass unmodulatedlight with virtually no attenuation, whereas typical liquid crystalcells significantly attenuate light. Similarly, MEMS optical modulator70 can provide much higher contrast ratios than liquid crystal cellsbecause MEMS shutters 72 are opaque and can provide complete modulationof the light. Finally, MEMS optical modulator 70 can be manufactured byconventional CMOS circuit techniques without requiring the complexprocesses typically required for liquid crystal displays.

In one implementation, for example, MEMS optical modulator 70 couldinclude a 200×200 array of MEMS shutters 72 for controlling lightpassing through a corresponding 200×200 array of apertures 74. In thisimplementation, for example, converging microlens array 60 could include200×200 lenslets 62 that each have a focal length of about 1 mm, andapertures 74 may be positioned in a right, regular array withseparations of about 50 μm between them. MEMS optical modulator 70 insuch an implementation could have dimensions of 1 cm×1 cm and thicknessof substrate 76 of about 200 μm. With lenslets 82 of projectionmicrolens array 80 providing magnification of about 2.5, display screen86 could have dimensions of about 2.5 cm×2.5 cm, or about 1 inch×1 inch.

FIG. 17 is a diagrammatic side view of a MEMS optical device module 100having converging microlens array 60 with a two-dimensional array oflenslets 62 (only one dimension shown), MEMS optical modulator 70, andprojection microlens array 80 with a two-dimensional array of lenslets82 (only one dimension shown). MEMS optical device module 100 is shownin relation to an illumination source, collimating lens and displayscreen (shown in dashed lines) to illustrate an exemplary displayapplication or use of module 100.

MEMS optical device module 100 includes a mounting structure (e.g., aframe or housing) 102 that contains or encompasses converging microlensarray 60, MEMS optical modulator 70, and projection microlens array 80.Mounting structure 102 allows MEMS optical device module 100 to fittogether with other such modules, either in a close packed arrangementor in secure engagement with each other. An electrical connection 104(e.g., a plug, socket, lead, etc.) allows a display controller (notshown) to be connected to MEMS optical modulator 70 to provide displaycontrol signals for controlling MEMS shutters 72. It will be appreciatedthat in other implementations, a MEMS optical device module of thisinvention could include any of an illumination source, collimatingoptics and a display screen.

FIG. 18 is a diagrammatic side view of a MEMS optical display system 120that includes a one- or two-dimensional array 122 (only one dimensionshown) of multiple MEMS optical device modules 100. In oneimplementation, all of MEMS optical device modules 100 are identical. Amodular display housing 124 supports and encloses array 122 of MEMSoptical device modules 100.

Modular display housing 124 includes a light source 126, a reflector128, and collimating optics 130 to provide collimated illumination tothe multiple MEMS optical device modules 100. To support a thin flatpanel form factor, light source 126 and reflector 128 could be analogousto those used in laptop computer flat panel displays, and collimatingoptics 130 could be a generally flat microlens array or Fresnel lens.

An integrated display controller 134 is electrically coupled toelectrical connections 104 of MEMS optical device modules 100 to provideintegrated control of modules 100 as a single display. (The electricalcouplings are not shown for purposes of clarity.) A transmissive,diffusive display screen 136 functions as an integral display screen forthe MEMS optical device modules 100 of array 122.

In an exemplary implementation, each MEMS optical device module 100provides a 200 pixel×200 pixel display over an area of 2.5 cm×2.5 cm. AMEMS optical display system 120 that includes a 6×8 array 122 of MEMSoptical device modules 100 would provide a 1200 pixel×1600 pixel displayover an area of 15 cm×20 cm.

For purposes of illustration, MEMS optical display system 50 and MEMSoptical device modules 100 are each shown with a diagrammatic lightsource 52. In monochromatic (e.g., black and white) implementations,light source 52 could correspond to a single (e.g., nominally white)light source (e.g., lamp). In polychromatic implementations, lightsource 52 could include one or more separately controlled light sourcesthat cooperate to provide polychromatic or full-color images.

FIG. 19 is a diagrammatic side view of a microelectrical mechanicalstructure (MEMS) optical display system 150 showing one implementationof a polychromatic illumination source 152 and an associated reflector154. Components of MEMS optical display system 150 that are generallythe same as those of display system 50 are indicated by the samereference numerals.

Illumination source 152 includes multiple (e.g., three) color componentlight sources (e.g., lamps) 156R, 156G, and 156B that are positionedgenerally in a line and generate red, green, and blue light,respectively. A display controller 158 that separately controls MEMSshutters 71 also activates color component light sources 156R, 156G, and156B separately. During times that it successively activates colorcomponent light sources 156R, 156G, and 156B, display controller 158applies control signals to MEMS shutters 72 corresponding to red, green,and blue image components, thereby to form color component images in afield-sequential manner.

For example, color component images that are generated at a rate of 180Hz can provide an image frame rate of 60 Hz. In one exemplaryimplementation, a display of 200×200 multi-color pixels could employmicrolens arrays 60 and 70 with 204×204 arrays of lenslets 62 and 72,respectively, to compensate for different optical paths taken bydifferent color components of light forming the display gamut. As analternative implementation, it will be appreciated that multiplesuccessive colors of illumination could be obtained by a spinning colorwheel and a while light source, as is known in the art.

FIGS. 20 and 21 are front views of an exemplary MEMS actuator 170 inrespective activated and relaxed states for controlling MEMS shutter 72.In this exemplary implementation, MEMS shutter 72 is maintained over itsassociated aperture 74 extending through MEMS substrate 76 when MEMSactuator 170 is in a relaxed state. MEMS shutter 72 is moved to notobstruct its associated aperture 74 when MEMS actuator 170 is in anactivated state. MEMS actuator 170 is one of a variety of MEMS actuatorsthat could be used to control MEMS shutter 72.

MEMS actuator 170 is an implementation of a thermal actuator, sometimescalled a heatuator, that functions as a pseudo-bimorph. Actuator 170includes a pair of structural anchors 172 and 174 that are secured to asubstrate (e.g., substrate 10 or nitride layer 12, not shown). A narrowsemiconductor (e.g., polysilicon) arm 178 is secured to anchor 172, anda wide semiconductor (e.g., polysilicon) arm 180 is secured to anchor174 through a narrow extension 182. Arms 178 and 180 are coupledtogether by a cross member 184. Except for attachments to anchors 172and 174, arms 178 and 180, extension 182, and cross member 184 arereleased from the substrate.

The components of actuator 170 have electrically semi-conductive andpositive coefficient of thermal expansion properties. For example,actuator 170 is formed of silicon. Actuator 170 is activated when anelectrical current is passed from a current source 190, such as a pixelcontrol signal source, through arms 178 and 180. The applied currentinduces ohmic or Joule heating of arms 178 and 180, causing them toexpand longitudinally due to the positive temperature coefficient ofexpansion of silicon. The smaller size of arm 178 causes it to expandmore than arm 180.

Actuator 170 utilizes differential thermal expansion of different-sizedarms 178 and 180 to produce a pseudo-bimorph that deflects in an arcparallel to the substrate. With actuator 170 in its relaxed state, asshown in FIG. 21, MEMS shutter 72 is positioned over aperture 74 andblocks light that is directed through it. With actuator 170 in itsactivated state, as shown in FIG. 20, MEMS shutter 72 is moved to allowlight to pass through aperture 74.

FIG. 22 is a diagrammatic side view of a microelectrical mechanicalstructure (MEMS) optical display system 200 that is the same as MEMSoptical display system 50, except that a microelectrical mechanicalstructure (MEMS) optical modulator 202 includes a two-dimensional arrayof microelectrical mechanical structure (MEMS) shutters 204 positionedon a light-receiving side 206 adjacent apertures 208. MEMS shutters 204may be controlled by MEMS actuators (not shown) that move within a planeparallel to optical modulator 202, as described above with reference toFIGS. 20 and 21.

In other implementations, MEMS shutters 72 and 204 of MEMS opticalmodulators 70 and 202 could be controlled by MEMS actuators that moveshutters 72 and 204 in planes that are transverse (e.g., perpendicular)to modulators 70 and 202, respectively. In such implementations,shutters 72 and 204 would have light-blocking positions at about thefocal points of lenslets 62. Shutters 72 and 204 would have generallylight-transmitting positions that are generally distant from the focalpoints, but still within the optical paths of the light.

FIG. 23 is a diagrammatic plan view of a microelectrical mechanicalout-of-plane thermal buckle-beam actuator 250 capable of providingtransverse-plane movement of shutters 72 and 204, as described above.Actuator 250 includes a pair of structural anchors 252 and 254 that aresecured to a substrate (e.g., substrate 10 or nitride layer 12, notshown) and one or more thermal buckle beams 256 (multiple shown) thatare secured at their base ends 260 and 262 to anchors 252 and 254,respectively. Buckle beams 256 are substantially the same and extendsubstantially parallel to and spaced-apart from the substrate and arereleased from it other than at anchors 252 and 254.

A pivot frame 264 includes a frame base 266 that is secured to bucklebeams 256 at coupling points 268 that in one implementation arepositioned between buckle beam midpoints (indicated by dashed line 270)and one of anchors 252 and 254 (e.g., anchor 254). Pivot frame 264further includes at least one pivot arm 272 (two shown) that is coupledto frame base 266 at one end and extends to a free end 274 that pivotsout-of-plane when actuator 250 is activated. Pivot frame 264 is releasedand free to move, other than where frame base 266 is secured to couplingpoints 268. FIG. 24 is a diagrammatic side view of actuator 250 in arelaxed state illustrating pivot frame 264 as being generally parallelto or co-planar with buckle beams 256.

Structural anchors 252 and 254 and buckle beams 256 have electricallysemi-conductive and positive coefficient of thermal expansionproperties. For example, buckle beams 256 are formed of silicon.Actuator 250 is activated when an electrical current is passed from acurrent source 280 through buckle beams 256 via electrically conductivecouplings 282 and 284 and structural anchors 252 and 254, respectively.The applied current induces ohmic or Joule heating of buckle beams 256,thereby causing them to expand longitudinally due to the positivetemperature coefficient of expansion of silicon. With anchors 252 and254 constraining base ends 260 and 262 of buckle beams 256, theexpanding buckle beams 256 ultimately buckle away from the substrate. Inone implementation, buckle beams 256 are formed to have a widened aspectratio, with widths (parallel to the substrate) greater than thethicknesses (perpendicular to the substrate), to provide a bias orpredisposition for buckling away from the substrate, rather thanparallel to it. FIG. 25 is a diagrammatic side view of actuator 250 inan activated state illustrating the out-of-plane buckling of bucklebeams 256.

The buckling of buckle beams 256 away from the substrate in the activestate of actuator 250 causes free end 274 of pivot frame 264 to pivotaway from the substrate. Pivot frame 264 rotates about frame base 266,which is also raised away from the substrate by buckle beams 256. As aresult, free end 274 moves and exerts a pivoting or rotational forceoutward away from the substrate. When the activation current ceases,buckle beams 256 cool and contract, which causes free end 274 of pivotframe 264 to return to its initial position with a force equal to theactuation force, but in opposite rotational and translationaldirections. Such rotational deflections of pivot frame 264 may be usedin a variety of applications, including providing out-of-planedeployment of other micro-mechanical structures, such as those used inmicro-optical devices. In the implementation illustrated in FIGS. 23-25,for example, a shutter 286 is secured to free end 274 and pivots withpivot frame 264 to selectively deflect light according to whetheractuator 250 is in its relaxed or activated state.

FIG. 24 shows buckle beam 256 in a relaxed state extending over aspacing pad 290 that is secured to and extends from substrate 10 (e.g.,the nitride layer 12) near the middle of buckle beam 256. FIG. 25 showsbuckle beam 256 in an activated state. For example, spacing pad 290 maybe formed of a P0 layer with a thickness of 0.5 μm, and buckle beam 256may be formed of a different (released) layer. Spacing pad 290 forces asmall (e.g., 0.5 μm) hump or deflection 294 in each of buckle beams 256due to the conformal nature of the fabrication. Also, a dimple 292 isformed near each end of buckle beam 256. Dimples 292 may be formed as aprotrusion or dimple extending from a bottom surface of buckle beam 256or as a recess into its top surface, or both, as illustrated. In a MUMPsimplementation, for example, dimple 292 may be formed as is a 0.5 μmdepression in the 2 μm poly1 layer and does not touch the substrate.

Spacing pad 290 and dimples 292 cause buckle beams 256 to buckle awayfrom the substrate and reduce the stiction between buckle beams 256 andthe substrate (e.g., the nitride layer 12). It will be appreciated thatfor the multiple buckle beams 256 in a typical actuator 250, a separatespacing pad 290 could be formed for each buckle beam 256 or spacing pad290 could be formed as a single continuous pad that extends beneath allthe buckle beams 256. Spacing pad 290 and dimples 292, eitherindividually or together, could be used alone or with a widened aspectration for buckle beams 256 to provide a bias or predisposition for themto buckle away from the substrate.

As described above, some implementations employ thermal MEMS actuators.Some thermal MEMS actuators can require significant power when activated(e.g., 10 mA), so that current requirements for simultaneous operationof many such actuators can be excessive. It will be appreciated,therefore, that other MEMS actuators, including at least electrostaticactuators and thermal actuators with reduced power requirements, may beused in other implementations to reduce the overall system powerrequirements. In addition, applications described above refer primarilyto optical display applications. It will be appreciated, however, thatvarious aspects of the present invention, including MEMS opticalmodulators 70 and MEMS optical device modules 100, could be used inother light modulating applications, such as modulated scanners,detectors, etc. In such applications, MEMS optical modulators 70 andMEMS optical device modules 100, for example, could employone-dimensional arrays of optical elements.

In one implementation described above, MEMS substrate 76 of MEMS opticalmodulator 70 has a thickness of about 200 μm. In mounting or supportingMEMS optical modulator 70 by its edges, such a thickness provides MEMSoptical modulator 70 with adequate structural rigidity. With apertures74 having dimensions across them of about 20 μm, lenslets 62 ofconverging microlens array 60 can require a relatively large depth offocus. To avoid such a large depth of focus, an alternativeimplementation of a MEMS optical modulator, such as MEMS opticalmodulator 202 in FIG. 22, could employ reflective pads, rather thanapertures, to selectively reflect illumination light from the reflectivepads to a display screen, scanner, sensors, etc.

Parts of the description of the preferred embodiment refer to steps ofthe MUMPs fabrication process described above. However, as stated, MUMPsis a general fabrication process that accommodates a wide range of MEMSdevice designs. Consequently, a fabrication process that is specificallydesigned for the present invention will likely include different steps,additional steps, different dimensions and thickness, and differentmaterials. Such specific fabrication processes are within the ken ofpersons skilled in the art of photolithographic processes and are not apart of the present invention.

In view of the many possible embodiments to which the principles of ourinvention may be applied, it should be recognized that the detailedembodiments are illustrative only and should not be taken as limitingthe scope of our invention. Rather, I claim as my invention all suchembodiments as may come within the scope and spirit of the followingclaims and equivalents thereto.

1. A microelectrical mechanical out-of-plane thermal buckle-beamactuator capable of providing transverse-plane movement of shutters,comprising: a pair of structural anchors secured to a substrate, thesubstrate defining a plane; and at least one thermal buckle beam securedat respective base ends to said anchors, said buckle beam extendingsubstantially parallel to and spaced-apart from the substrate andreleasable from the substrate, other than at said anchors, in adirection transverse to the plane.
 2. A microelectrical mechanicalout-of-plane thermal buckle-beam actuator as recited in claim 1, furthercomprising: a pivot frame including a frame base secured to said bucklebeam at a coupling point positioned between a buckle beam midpoint andone of said anchors.
 3. A microelectrical mechanical out-of-planethermal buckle-beam actuator as recited in claim 2, wherein said pivotframe further comprises at least one pivot arm coupled to said framebase at one end and extending to a free end that is pivotableout-of-plane.
 4. A microelectrical mechanical out-of-plane thermalbuckle-beam actuator as recited in claim 3, wherein said pivot frame isreleased and free to move, other than where said frame base is securedto said coupling point.
 5. A microelectrical mechanical out-of-planethermal buckle-beam actuator as recited in claim 1, wherein saidstructural anchors and at least one thermal buckle beam compriseelectrically semi-conductive and positive coefficient of thermalexpansion properties.
 6. A microelectrical mechanical out-of-planethermal buckle-beam actuator as recited in claim 5, wherein said atleast one thermal buckle beam is formed of silicon and the actuator isactivatable by supplying an electrical activation current through saidbuckle beam, thereby causing said buckle beam to expand longitudinallydue to the positive temperature coefficient of expansion of silicon andbuckling away from the substrate.
 7. A microelectrical mechanicalout-of-plane thermal buckle-beam actuator as recited in claim 6, whereinsaid at least one buckle beam is formed so as to have a widened aspectratio, with its width parallel to the substrate) greater than itsthickness (perpendicular to the substrate), thus providing a bias forbuckling away from the substrate rather than parallel to it.
 8. Amicroelectrical mechanical out-of-plane thermal buckle-beam actuator asrecited in claim 7, wherein buckling of said at least one buckle beamaway from said substrate in the activated state of the actuator causes afree end of said pivot frame to pivot away from the substrate.
 9. Amicroelectrical mechanical out-of-plane thermal buckle-beam actuator asrecited in claim 8, wherein said pivot frame is rotatable about saidframe base, and the free end is movable so as to exert a pivoting forceoutward away from the substrate.
 10. A microelectrical mechanicalout-of-plane thermal buckle-beam actuator as recited in claim 9, whereinsaid at least one buckle beam cools and contracts when said electricalactivation current ceases, thereby causing the free end of said pivotframe to return to its initial position.